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S1 Normal Distribution Question
hi, can anyone help me for my exam tomorrow, I cant really work it out from the markscheme so if anyone could explain i would really appreciate it thanks!
Sunflower height is normally distributed mean 185 and standard deviation 10
Determine the probability that the mean height of a random sample of 4 sunflowers is more than 190cm.
thanks a lot! x
Sunflower height is normally distributed mean 185 and standard deviation 10
Determine the probability that the mean height of a random sample of 4 sunflowers is more than 190cm.
thanks a lot! x
Reply 1
First you have to standardize, it so u can work out the z score.
So its x - mu / sigma (st dev which is 10/the square root of 4)
190 - 185 / 10 = z < 1 then just read of the z score from your tables
is this what it says in your mark scheme?
So its x - mu / sigma (st dev which is 10/the square root of 4)
190 - 185 / 10 = z < 1 then just read of the z score from your tables
is this what it says in your mark scheme?
Reply 2
ssp123
OP
oooooooo i see.. it said that but it didnt say about finding the standard dev, just the calculation so i was a bit confused. thanks a lot mate! x
Reply 3
ssp123
OP
actually my bad it says..
(190-185)/5 as (10^2)/4=25
what formula did u use to calculate variance when given mean? x
(190-185)/5 as (10^2)/4=25
what formula did u use to calculate variance when given mean? x
Reply 4
Im not quite sure what your looking for here. Is the distribution approximately normal? then the variance is st dev squared divided by n.
Did i actually get the question wrong then?
Did i actually get the question wrong then?
Reply 5
omg!!! i just started a thread asking the exact same question! LOL
Reply 6
ssp123
OP
yes mate u are right but as its standard deviation squared divided by n, its 10 squared over 4 which is 25. which means sd is 5 not 10. so it is 190-185 all over 5 which is 1 which is the right answer, cheers for your help x
Reply 7
Ahhhhh right yehh i see. Thanx for clearing that up.
Good Luck tomorrow !!!!!
Good Luck tomorrow !!!!!
Reply 8
ssp123
OP
its cool man, thanks 
x
xReply 9
Hi, how could I do this with a graphical calculator? (Casio fx-9750GII if it helps) Thanks
Reply 10
Never mind, I worked it out.
(For the benefit of anyone else who needs it, you do Normal C.D., set the lower to 190, upper to 1000000, sigma to 5 and mu to 185 and it'll give you the right answer)
(For the benefit of anyone else who needs it, you do Normal C.D., set the lower to 190, upper to 1000000, sigma to 5 and mu to 185 and it'll give you the right answer)
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